From the ages of 16 to 18, John Walker had transformed himself from a quiet, smooth-cheeked American teenager to a devout, bearded Muslim studying in Yemen. That he could grow the requisite beard was something of a miracle. Were his parents really onboard with all this? With the new name? The move to Yemen? Frank Lindh says yes. "He was always intellectually coherent, and he had a wonderful sense of humor," Lindh told reporters. "And none of that changed when he converted to Islam. I never had any major misgivings."

When Walker returned to California around Christmas 1999, he found his parents had separated. He saw Nana and told him that Yemen hadn't met his expectations. "They weren't as orthodox as he thought--they weren't as strict on Islam as he thought," says Nana. But to Abdul Wadood, a 20-year-old Muslim friend who also met Walker at the Mill Valley mosque, John sounded fulfilled. Through his e-mail communications, he told Wadood he felt "free" because he didn't have any material possessions. Wadood says his friend never experienced culture shock because he was so "open-minded." But Walker may have also been a bit too trusting. He just "let anybody in," says Wadood.

When the U.S.S. Cole was bombed in October 2000, Walker was back in Yemen. In an e-mail exchange with his son, Frank Lindh said he felt terrible for the victims and their families. John's reply suggested that the attack may have been justified because the Cole was docked in an Islamic country. Lindh dismissed the exchange as a "father/son debate, much like my dad and I used to have over [the] Vietnam war." A month after the Cole bombing, Walker left Yemen for Bannu, a village in Pakistan's northwest, to attend an Islamic school, or madrasah. Pakistan's madrasahs specialize in teaching students to memorize the Koran. They are also reputed to provide thousands of soldiers for the Taliban.

John Walker's last contact with his family was in May 2001. He told his mother he was leaving Bannu and "moving somewhere cooler for the summer." He asked his father for money, and Frank Lindh sent him $1,200. It wasn't long before Marilyn Walker wondered just where her son had gone. In early summer, she contacted John's madrasah. According to the Marin Independent Journal, a teacher there wrote her back on July 27, saying John, whom he called Sulayman Faris, arrived at the school on Nov. 30, 2000, and "impressed [everyone] with his character" during his stay. On May 15 he was apparently turned over to the care of the missionary who had originally brought him to the school. No one knew where John was.

Sept. 11 came and went, and still John's parents heard nothing. Finally, on Dec. 1, Marilyn Walker and Frank Lindh saw their son on television. As the footage played, Marilyn Walker burst into tears. John was filthy and had a bullet wound in his leg. In a husky voice and accented English, John told CNN where he had been the past six months. "I was a student in Pakistan, studying Islam, and came into contact with many people connected with the Taliban," he said. "The people in general have a great love for the Taliban. So I started to read some of the literature of the scholars, the history of Kabul. My heart became attached to that." John said he had been sent to an Arabic-speaking al-Qaeda camp, where he learned to shoot a Kalashnikov. He saw Osama bin Laden several times. He answered the call to jihad and fought in Kashmir and Kunduz. Then he became a prisoner of war.

John Walker's case is strange, but it may not be unique. The Defense Department is looking for two other Americans rumored to have fought for the Taliban. Walker is now in the custody of the U.S. military, and late Saturday the Pentagon said he is being held at Camp Rhino in Afghanistan. "What we really want is some communication with them as to how he is," says the family's recently hired attorney, James Brosnahan. The family's concern is not the government's top priority.